Clean energy vehicles using fuel gases, such as a hydrogen gas and a natural gas, are known, and examples thereof include fuel-cell vehicles, hydrogen engine vehicles, and natural gas vehicles. The clean energy vehicle includes a high-pressure tank and one of an injector and an electromagnetic pressure regulating valve and runs in such a manner that the fuel gas stored in the high-pressure tank is supplied by the injector or the electromagnetic pressure regulating valve to a fuel cell or a gas engine. Each of the injector and the electromagnetic pressure regulating valve can adjust the flow rate (or the pressure) of the fuel gas supplied to the fuel cell or the gas engine. The output of the fuel cell or the gas engine is controlled by adjusting the flow rate (or the pressure) of the fuel gas by the injector or the electromagnetic pressure regulating valve.
The injector can close and open an injection hole thereof to adjust the flow rate of the fuel gas. The injector changes the flow rate of the fuel gas by a ratio between an open time of the injection hole and a closed time of the injection hole, that is, a duty ratio. If differential pressure between upstream pressure of the injector and output pressure of the injector is high, the flow rate of the fuel gas which flows when the injection hole of the injector is opened is extremely high, and the change in the flow rate of the fuel gas with respect to the change in the duty ratio of the injector is significant. Especially, in a low flow rate region (the fuel cell or the gas engine is in a low load state), a flow gain (a value obtained by dividing the flow rate of the fuel gas by the duty ratio) is large, and the control operation is difficult. In addition, another problem is that if the upstream pressure of the injector increases, the span of duty control for changing from a low flow rate to a high flow rate becomes extremely narrow.
The electromagnetic pressure regulating valve can adjust the opening degree (opening area) of a valve passage to adjust the flow rate of the fuel gas. Therefore, if the upstream pressure of the electromagnetic pressure regulating valve increases, differential pressure between an upstream side and downstream side of the electromagnetic pressure regulating valve increases. On this account, the flow rate of the fuel gas significantly changes only by slightly increasing the opening degree, and the change in the flow rate of the fuel gas with respect to the change in the opening degree of the valve passage is significant. Therefore, as with the injector, in the electromagnetic pressure regulating valve, the pressure control of the fuel gas in the low flow rate region (low load state) is extremely difficult.
To solve such difficult problems, two regulators are provided upstream of an injector in a fuel cell system disclosed in PTL 1. These two regulators are arranged in series and reduce the pressure of a hydrogen gas in two stages, the hydrogen gas being supplied from a high-pressure tank. In the fuel cell system, the upstream pressure of the injector is maintained at certain low pressure or lower by the two regulators, so that differential pressure between an upstream side and downstream side of the injector is low. Thus, the pressure controllability is secured. The fuel cell system includes a shutoff valve provided upstream of the two regulators. The shutoff valve can shut off communication between the hydrogen tank and the fuel cell to stop the supply of the hydrogen gas.